This invention relates to phthalide derivatives as new compounds useful as colorless chromogenic materials, a new process for preparing the same, and a new recording system utilizing the same.
There are known various kinds of recording systems utilizing the colorforming reaction between a colorless chromogenic material and an electron accepting acidic reactant material by the medium of mechanical, heat, electric or light energy. Among them there are included a pressure sensitive record sheet, a heat sensitive record sheet, an electrothermal record sheet, an ultrasonic record sheet, an electron beam record sheet, an electrostatic record sheet and a photosensitive record sheet. The colorless chromogenic materials of these kinds also find their usefulness in typewriter ribbons, ball-point pen ink, crayon and stamp ink.
One of the most typical colorless chromogenic materials is crystal violet lactone. This dye material reacts with an electron accepting acidic reactant material upon contact to develop a clear color of bluish violet but the developed color has a poor light resistance so that the recorded images (color images) soon disappear in a short time when subjected to radiation of ultraviolet rays of day light. Another disadvantage of this type of dye is in the fact that the recorded images obtained with this material show no absorption for the infrared range of 700-900 nm and accordingly this type of dye material cannot be used for a reading machine utilizing an optical reading system responsive to infrared absorption.
Recently, we have proposed certain kinds of phthalide derivatives having two vinyl linkages as substantially colorless chromogenic material which are adapted for optical reading with near infrared rays in EP Application No. 82301885.8 (EP Publication No. 62544).
However, the record materials such as heat-sensitive record materials in which any of those phthalide derivatives is used are easily affected by temperature and humidity so that fogging occures and the produced color image is discolored. Resultantly, the difference between the light absorptions of the produced color image and the background at near infrared wavelength become too small to adapt them for optical reading. Further, if the produced color images exposes to light, the light absorbability of near infrared wavelength is liable to disappear so that it become difficult to adapt them for optical reading as described above. In addition, color developing on the background and discoloration of the produced color images easily occur by finger-print.
The primary object of the invention is to provide novel phthalide derivatives superior in both of heat resistance and moisture resistance and useful as colorless chromogenic materials for use in various recording systems.
Another object of the invention is to provide novel colorless chromogenic material for use in recording systems in which the color images when developed therefrom have a good light resistance, especially, a good ultraviolet ray resistance.
A further object of the invention is to provide novel colorless chromogenic materials for use in recording systems in which the color images when developed therefrom show a good absorption for infrared rays.
A still further object of the invention is to provide a novel process for preparing phthalide derivatives of the kind described above.
It is also included among the objects of the invention to provide an improved recording system in which a phthalide derivative as a new compound is used as a colorless chromogenic material and the color images when developed therefrom have a good light resistance and show a good absorption for infrared rays.
Other objects and advantages of the invention will become apparent from the following description.